Will Composite Decking Warp – How to Fix?

does composite decking warp

For years decks were made primarily from wood. One of the main downsides of wood has always been its vulnerability to heat and moisture.

However, in recent years, composite timber has become a hot choice for usage in deck construction, and to a large degree, it has helped address the common issues with wood.

But do composite decking materials also warp?

The honest answer is that yes, composite does warp, but the upside is that it does so at a far slower rate than traditional wood decking.

Composite timber, like the popular one Trex, offers many new decking options.

These various composite decks will warp with time and exposure to the elements, but as not all composite materials for decks are created equal, they all have different warping tendencies.

The factors that decide how soon the warping can start include the composite materials’ plank density, constitution, the quality of their engineering, joist spacing, and strength of synthetic binders.

Environmental elements are a big factor in the warping of composite decking too of course, but there is also a human element involved.

The more care that the deck owner applies to their decking composite, the less frequently warping of the material will occur as a general rule of thumb.

Types Of Warping in Decks

If a composite deck begins to warp, there are generally 5 ways in which it begins to manifest.


The edges of the deck begin to bend inwards while the middle remains flat, forming a shape of a bow.


Often resembling a twisted ribbon, this type of warping is when the wood begins to twist inwards at both ends.


When only one end of a plank is exposed to significant levels of moisture, it tends to be the only one that begins to bend inwards.

The shape of bending only one side ends up taking the upper shape of a letter C, resembling a crook.


This is a more extreme version of warping.

In this type of warping, the material begins to curl inwards toward the deck’s center and begins to resemble the shape of an upside-down cup.


The kink is when the decking material begins to bend upward on one side, resembling an arm flexed at the elbow.

In a way, it is the polar opposite of a crook.

how to fix hollow composite decking problems

Causes Of Warping in Composite Decking

There tend to be 5 primary causes for the warping of composite decking material:

1- Plank Density

When the density of plank material is strong, so is the resistance to warping.

The composition of the composite material directly affects the levels of density and/or their hollowness.

For instance, those composites formed from high-density polyethylene and a softwood chips mixture are of a lesser density than that composed of recycled hardwood and high-density polypropylene.

2- Weather

Composite decking that is unprotected from the elements tends to be affected by warping vulnerabilities more frequently.

Wind, sunlight, rain, humidity, and dryness, as well as cold and warm weather extremes, directly affect the integrity of the material.

Perpetual exposure expedites the warping potential of the composite material.

For instance, constant exposure to rain leads to quicker development of rot which ends up the deck beginning to experience curving.

When the weather changes abruptly from warm to cold or vice versa, lumber expands or contracts, which causes integrity damage as well.

Persistent exposure to the sun’s UV rays also affects decking because it wears away the synthetic binders that keep the composite material together.

As these wear down, the material becomes weaker and therefore more susceptible to warping.

3- Poor Joist Spacing

The joists support the entire structure of the deck, serving, essentially as the deck’s bones.

One of the most important things during the process of deck construction is the placement of joists with sufficient space between them in order to properly balance the weight of the planks on the deck.

There is however no one perfect method for joist spacing.

Every deck requires slightly different joist spacing.

However, the improper arrangement of joists does have a common downside of affecting the integrity of decks.

There are some typical joist install rules of thumb in decking.

For instance, residential decks should not exceed 16 inches between the centers of the joists, while commercial decking cuts that distance between joists to just 1 foot.

Because stairs and landings typically absorb more weight on smaller spaces, the joists underneath them should be more tightly packed together.

When the spacing between joists is too large, it to the additional stress on the boards, which, in turn, leads to higher chances of warping.

4- Poor Deck Maintenance

There are many preventable, easy-to-take actions that people can do to extend the life of composite decks, but many simply avoid them.

For instance, spilled liquids or water pooling, if not mopped up, eventually get absorbed by the material which slowly (but surely) promotes rot.

Using planks that are untreated for construction is another common error made.

Failing to adequately adjust loose screws to the joists under the deck or simply subjecting the deck to far too much weight are other common poor deck maintenance habits as well.

5- Type of Composite Decking and its Constitution

Recycled wood and plastic are the main components that comprise composite materials.

However, the type of wood flour and plastic type that is at their source varies.

Some of the wood sourcing includes hardwood flour, softwood flour, or bamboo flour.

The plastics can also be made from polyethylene or polypropylene.

Any mixture of these, as well as usage of plywood, PVC, or natural wood/bamboo fibers, result in a different constitution of composite decking materials.

The particular mixture and makeup for the composite material are directly tied to the tensile strength of the material.

When the constitution is subpar, the decking material is weaker and more vulnerable to breaks and warps.

Those decks composed of the strongest materials hold out far more than their weaker counterparts.

how to fix warped deck boards

Identifying And Repairing Warped Composite Decking

If the composite decking is less flat and straight now than it was at the time of original installation to the naked eye, it is likely that warping has begun.

You can pretty easily tell when the planks are further removed from one another.

This distancing is essentially the start of warping.

To repair warped composite decking issues.

If you are savvy with power tools like saws or have a handy friend who can help you out, there are a few good methods to attacking the repair of warped composite decking.

The tools you will likely need are a power saw, claw bar, screw gun, replacement planks, tape measurer, and of course, safety goggles.

Once you have the necessary tools and safety gear together, you need to next look under your deck to check out the joists.

These will be made of wood even sitting underneath composite decking so they should be easy to spot.

These will be the support planks that underlie the decking itself.

Step 1: Measure the Plank

Carefully observe the deck to identify the planks that are warping.

Once a plank is identified, measure the plank with your tape measurer to the most accurate measurement you can assess.

This will inform you as to the depth that you will need to make when you cut your replacement plank with your circular saw.

Based on what the plank measures, is how much you cut into your replacement plank Usually these are about 1 inch in depth.

Step 2: Cut the Plank

After setting your circular saw to the plank’s desired depth, put on your safety goggles to avoid flying debris getting in your eyes.

Remember to cut lengthwise, not width-wise. Then start sawing the warped plank with the circular saw.

Just make sure you stop before you reach the joist, or you will have another repair on your hands.

Step 3: Pry it Open

With a straight cut through the warped plank, you will next need to get your claw bar (or a crowbar if unavailable), though claw bars are easier.

Insert the bar into the composite plank that has now been split but your cut.

After lining it up directly in the cut line, pry hard to separate the two portions of the plank. This will allow you to remove it easily.

Step 4: Remove the Plank

After the composite deck is split you should use your screw gun to detach all of the screws along the line of the plank that connects to a joist, removing the plank completely once they are all detached.

Assuming the split was clean, you can then measure the plank in order to find out what size to cut the replacement plank to.

If there is too much damage, just measure a plank that is in good shape accurately.

This way you know that you will cut a replacement specifically to fit in the place of the old one.

Step 5: Replace the Plank

Once you know the size of the replacement, you will need to cut the new plank to replace the warped one.

Measure out the new decking piece, cutting off the excess length in order to make it a perfect fit for your deck.

Lay the new piece in the place of the recently removed one and use the screw gone to adjoin the new plank to the joists beneath.

You can then repeat this process for any other warped planks.

Final Thoughts

Replacement of warped planks on a composite deck does not require you to spend tons of money on hiring help.

Most people are completely capable of saving a lot of money by fixing and straightening it on their own.

However, if there is an issue with the joists or every plank on your deck is warped, investing in professional assistance is the better alternative.

This occurrence is rare, but it could indicate whether factors are significant or faulty initial installation.

Since you will already be exposing the joists, it’s a good idea to check on how they are holding up.

After all, they are your deck’s skeletal system, and sturdy bones are good for holding the body together.

If you follow the above steps and take your time to cautiously measure and cut new planks for your deck, you can surely replace the warped planks on your own.

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